1. Field of the Invention
The present invention relates to a semiconductor memory device, such as a memory card incorporating a mask ROM as a read only memory (hereinafter “ROM”), especially a semiconductor memory device, of which defective part produced at the time of writing in the ROM is replaced by normal part to reduce the fraction defective and increase the production yield.
2. Description of the Related Art
Japanese Patent Application Kokai Numbers 8-115175 and 2000-10870 disclose a conventional semiconductor memory device having a remedy of defective part.
The technology of a semiconductor disk, which is one of the semiconductor memory device, is disclosed in these references. The semiconductor disk comprises a readable/writable non-volatile flash memory. When defective part is produced in the flash memory during writing or reading of data, the defective part is replaced by normal part to reduce the fraction defective and increase the production yield.
However, it is a defective remedy technology for the flash memory. There has been no appropriate semiconductor memory device, such as a read only memory card incorporating a ROM, having a defective remedy means. The flash memory with a large memory capacity is expensive because of its sophisticated structure. By contrast, the read only semiconductor memory device is not expensive and easy to increase the memory capacity because of its simple structure. Accordingly, a defective remedy for the read only semiconductor device has been demanded.